Sleep tracking accuracy ios16

Thanks JJ. Part of the reason for the post was the YouTube video by "The Quantified Scientist" where he analysed the Apple Watch algorithm when WatchOS 9 came out. He rated the Apple Watch as the best wearable for sleep tracking. I accept his results because he's very scientific but then I noticed that the Apple Watch was consistently reporting less deep sleep than other algorithms which on its own does not mean the algorithm is wrong. However the Apple Watch also consistently reports lower deep sleep scores than are considered normal for healthy adults and this means more investigation is needed. I belong to a biohacking group on whatsapp and I did a survey monkey survey on it - I got 15 responses. The most popular device was Oura ring followed by Whoop, Fitbit, and Garmin. All of the other devices consistently report higher deep sleep scores than the Apple Watch. In my own case when I used the Autosleep algorithm it was reporting 30-90 minutes of deep sleep. When I switched to the native Apple algorithm it is reporting as little as zero deep sleep and never more than 40 minutes (and this was after a long-haul flight when I slept for about 10 hours straight). I'm pretty healthy, I train every day, don't smoke, don't drink and have a relatively low stress life so I don't think the Apple algorithm is working for me.